1. Technical Field
The present invention relates to particles and a method for producing particles, using a method for plasticizing a pressure plastic material with a compressive fluid, a toner containing the pressure plastic material, and a method for producing a toner, a developer containing the toner, a process cartridge, an image forming method, and an image forming apparatus, using the toner.
2. Background Art
Resins are roughly classified into thermoplastic resins and thermosetting resins. The thermoplastic resins are formed of a solid chain polymer, and reversibly repeat softening (plasticizing) by heating and curing by cooling. Examples of the thermoplastic resins include polyethylene, polypropylene, and polyvinyl chloride. On the other hand, the thermosetting resins have three dimensionally crosslinked network structures, and are solidified by curing reaction caused by heating two liquid components. Examples of the thermosetting resins include phenol resins, urea resins, unsaturated polyester resins, epoxy resins, and polyurethane. The thermoplastic resins and the thermosetting resins are respectively processed based on physical properties of the respective resins.
The thermoplastic resins have been processed by heating the thermoplastic resins at a temperature equal to or higher than the glass transition temperature (Tg) for plasticization, or heating the thermoplastic resins at a temperature equal to or higher than the melting point for melting, in order to decrease viscosity, and emulsify the thermoplastic resins in a fluidized state. However, there are many problems as follows: cost increases by the heat treatment; durability of the thermoplastic resin decreases due to degradation thereof, molecular weight of the thermoplastic resin decreases due to cutting of a molecular chain thereof; the thermoplastic resin is colored or decreases its transparency due to oxidation thereof, and the like (For example, see PTLs 1 to 5).
Particularly, in polymerized products obtained by polymerizing a ring-opening monomer, a molecular chain is easily cut due to back-biting in a melted state, and a decomposed product causes to form a foreign matter upon formation and to deteriorate the physical properties of a resin (a glass transition temperature and a melt viscosity), and significantly degrading molding processability and heat stability (NPL 1). Examples of the polymerized products obtained by polymerizing a ring-opening monomer include polylactic acid formed using lactide as a starting material, and polycaprolactone formed using ε-caprolactone as a starting material. These are classified into polyesters. Of these, polylactic acid has been desired to use as resin particles including use as a toner, because lactide (cyclic diester) as the starting material can be produced from a natural product, and is a plastic having balanced hue and mechanical strength.
As an exemplary product using the thermoplastic resin is a toner. In order to produce such toner, it is necessary to heat a toner material at a temperature higher than a glass transition temperature or melting point of the thermoplastic resin which is included in the toner (see PTLs 6 and 7). The heat treatment for toner production causes high cost, and degradation of the thermoplastic resin contained in the toner, causing decrease in durability thereof, and variation in molecular weight distribution thereof. These cause degradation of basic properties of the toner, such as charging ability, fixing ability, heat resistant storage stability (variation with time).
Therefore, in the present situation, a toner, which has excellent basic properties such as charging, variation with time, and the like, can reduce environmental load without generating waste liquid upon production, and can produce at low cost with no drying needed for production thereof, has not been provided yet. There is a demand for developing a new method for plasticizing a resin, and a method for producing a toner using the method for plasticizing a resin.